Conventionally, there is known an indwelling needle assembly in which an inner needle of an inner needle unit is attached so as to pass through an outer needle of an outer needle unit.
When performing fluid transfusion, blood collection, blood dialysis, for example, the indwelling needle assembly is configured to puncture a blood vessel of the patient, and then, by detaching the inner needle unit including the inner needle from the outer needle unit including the outer needle, the outer needle is left in the blood vessel of the patient to be used for treatment.
Meanwhile, with such indwelling needle assembly, in order to prevent inadvertent pricking due to the inner needle of the inner needle unit detached from the outer needle unit after the puncture, it is desirable to mount a needle tip protector for covering the needle tip of the inner needle unit. Accordingly, the specification of U.S. Publication No. US 2014/0025009 (Patent Document 1) and Japanese Patent No. JP-B-4994775 (Patent Document 2) disclose an indwelling needle assembly in which an inner needle unit is inserted into an outer needle unit and an outer-needle-hub engaging part provided to a needle tip protector is engaged with an outer needle hub of the outer needle unit. After the puncture of such indwelling needle assembly, in conjunction with the inner needle being pulled out of the outer needle, the needle tip of the inner needle is configured to be covered by the needle tip protector while engagement of the outer needle hub with the outer-needle-hub engaging part is allowed to be released.
Specifically, the needle tip protector described in these Patent Document 1 and Patent Document 2 is provided with a protection part that covers the needle tip of the inner needle due to pulling out of the inner needle. The protection part is pressed against a sleeve that covers the periphery of the inner needle from the lateral side induced by urging force due to gravity or elastic force. By so doing, when the inner needle is pulled out of the outer needle, the inner needle can be pulled out without directly rubbing against the protection part. This will minimize occurrence of troubles such that when the inner needle is pulled out, the sliding resistance (friction) to the protection part increases and the outer needle is unintentionally pulled out of the skin of the patient together with the inner needle being pulled out.
However, with the needle tip protector described in FIG. 4 etc. of Patent Document 1, a spherical body is adopted as the protection part, and since the spherical body moves due to the gravity, there is a risk that the protection mechanism will not work stably with respect to some orientations for which the indwelling needle assembly is used. Besides, if the spherical body overrides the needle tip of the inner needle or the like, the inner needle will be permitted to move towards the distal end side, posing a risk of the needle tip of the inner needle being exposed again. Moreover, with the needle tip protector described in FIG. 29 etc. of Patent Document 1, there is shown a mode wherein the outer-needle-hub engaging part and the protection part provided to the needle tip protector are opposed to each other sandwiching the peripheral wall of the outer needle hub from the outside and the inside. If the protection part rotates by 90° relative to the outer-needle-hub engaging part from the state shown in FIG. 29 due to external force or the like, for example, the gap between the protection part and the inner surface of the outer needle hub becomes large, and there is a risk that the engagement of the outer-needle-hub engaging part with the outer needle hub will be unexpectedly released before the inner needle is completely pulled out. Furthermore, with the needle tip protector described in FIG. 43 etc. of Patent Document 1, the needle tip protector is inserted in a concave part within the outer needle hub so that the outer needle hub and the needle tip protector are engaged. However, since the concave part is formed within the outer needle hub, dimensional errors are likely to occur, and some dimensional errors cause a risk of insufficient engaging force between the outer needle hub and the needle tip protector. Additionally, since the needle tip protector is inserted in the outer needle hub, in the case where a hemostasis valve or the like is provided to the outer needle hub, it is difficult to obtain enough space for it. This will inevitably increase the size of the outer needle hub.
Also, with the needle tip protector described in Patent Document 2, a coil spring is adopted as an urging member that presses the protection part against the sleeve. This may pose a problem of increase in the number of parts such as the coil spring, and a component for accommodating the coil spring.